1. Field of the Invention
The present invention relates to a hard disk drive, and, more particularly, to a technique for reducing a read channel optimization time.
2. Description of the Related Art
Recently, a data storage device has required a high capacity and a high access speed, in order to meet the needs of a multimedia system. For example, a hard disk drive (HDD) is one of the typical data storage devices. With an advantage of the high capacity and high access speed, the hard disk drive is widely used as an auxiliary memory for a computer system. Exemplars of recent efforts in the art include such designs as, for example, that shown by U.S. Pat. No. 5,247,254 to Huber et al., entitled Data Recording System Incorporating Flaw Detection Circuitry, U.S. Pat. No. 5,610,776 to Oh, entitled Method Of Optimizing Read Channel Of Disk Drive Recording Apparatus By Using Error, Rate, U.S. Pat. No. 5,440,433 to Yun, entitled Circuit And Method For Adjusting A Data Detecting Level Of A Disk Driving Apparatus, U.S. Pat. No. 5,087,992 to Dahandeh et al., entitled Method For Assigning Tracks On A Magnetic Data Storage Disk To Different Read/Write Frequency Zones, U.S. Pat. No. 5,532,586 to Ishikawa, entitled Method And Apparatus For Detecting Magnetic Disk Defects Using A Complete Disk Erasure Magnet, U.S. Pat. No. 5,471,351 to Ishiguro, entitled Method And Apparatus Of Verifying Accurate Writing Through Comparisons Of Written And Read Data, U.S. Pat. No. 5,537,264 to Pinteric, entitled Method For Optimally Selecting Media Transfer Rates For Different Data Heads Based on Individual Data Head Performance, U.S. Pat. No. 5,408,367 to Emo, entitled Method Of Optimizing Operation Of Disk Drive, U.S. Pat. No. 5,657,176 to Moribe et al., entitled Method And Apparatus For Optimizing The Recording And Reproducing Of Information From Magnetic Disks, U.S. Pat. No. 5,121,260 to Asakawa et al., entitled Read Channel Optimization System, U.S. Pat. No. 5,047,874 to Yomtoubian, entitled Technique For Certifying Disk Recording Surface, and U.S. Pat. No. 5,687,036 to Kassab, entitled Selection Of Optimum Write Current In A Disk Drive To Minimize The Occurrence Of Repeatable Read Errors.
Typically, with these and other designs, a hard disk drive is manufactured by a series of processes which may be classified into six large steps, such as illustrated in FIG. 1. Referring to FIG. 1, in a head disk assembly (HDA) assembling process, a first step I, a head disk assembly is assembled in a clean room, the head disk assembly being a part of the hard disk drive. In a servo write process, a second step II, a servo pattern is written on a disk for a servo control of a magnetic head for reading/writing data on a recording medium, e.g., a disk. The servo write process is performed by a servo writer. In a function test process, a third step III, the head disk assembly is combined with a printed circuit board (PCBA) and a determination is made as to whether or not the head disk assembly is well matched with the printed circuit board. In a burn-in test process, a fourth step IV, is to place the hard disk drive is placed on a rack in a burn-in room having a high temperature and a high humidity, and a program (i.e., firmware) is executed for a long time (commonly from eight to sixteen hours). The burn-in test process checks for defect sectors existing on the disk and takes a proper measure to have the defect sectors not used when the hard disk drive is actually used, so that a user may use the hard disk drive without trouble. Further, the burn-in test process includes a step of optimizing a read channel of the hard disk drive. In a final test process, a fifth step V, a determination is made as to whether or not the defect sectors of the hard disk drive set that have passed the burn-in test are correctly marked, by using a particular test system. After completion of the final test process, the hard disk drive set is sent out as a product by way of a sending-out test process, and a packaging and sending-out process, i.e., the sixth step VI.
In such a hard disk drive assembly as can be used in the practice of the present invention, for example, referring to FIG. 2, a plurality of disks 10 are rotated by a spindle motor 34. A plurality of heads 12 are respectively placed on corresponding disk surfaces of the disks 10. The heads 12 are mounted on support arms extending toward the disks 10 from an E-block assembly 14 associated with a rotary voice coil actuator 30. A preamplifier 16 preamplifies a signal picked up by one of the heads 12 and transfers the amplified analog signal to a read/write channel circuit 18 in a read mode, and writes encoded write data received from the read/write channel circuit 18 on the disks 10 through a corresponding one of the heads 12 in a write mode. The read/write channel circuit 18 detects and decodes a data pulse from the read signal received from the preamplifier 16 and supplies it to a disk data controller (DDC) 20, and/or decodes write data received from the disk data controller 20 and supplies it to the preamplifier 16. The disk data controller 20 writes data received from a host computer on the disks 10 via the read/write channel circuit 18 and the preamplifier 16, and/or transfers data read from the disks 10 to the host computer. Further, the disk data controller 20 interfaces a communication between the host computer and a microcontroller 24. A buffer RAM (Random Access Memory) 22 temporarily stores data being transferred among the host computer, the microcontroller 24, and the read/write channel circuit 18. The microcontroller 24 controls a track seek and a track following in response to a read or write command received from the host computer. A memory 26 stores an execution program of the microcontroller 24 and various setting values. A VCM driver 28 generates a driving current for driving the actuator 30 in response to a head position control signal generated from the microcontroller 24. The driving current generated from the VCM driver 28 is supplied to the actuator 30. The actuator moves the heads 12 on the disks 10 according to a direction and level of the driving current received from the VCM driver 28. A spindle motor driver 32 drives the spindle motor 34 according to a disk rotation control signal generated by the microcontroller 24.
The read/write channel circuit 18 reads data written on the disk 10 and converts it into digital data. Here, how accurately the read/write channel circuit 18 can read the analog signal transferred from the disk 10 via the head 12 is dependent on various parameters of the respective circuit elements in the read/write channel circuit 18. For examples, the parameters are a cut-off frequency, a group delay, a boost level, and a data threshold. When the parameters are optimally set, the host computer can read the data written on the disks 10, with the minimum errors. However, the optimal parameters do not have fixed values, and are slightly variable according to the respective hard disk drives. Further, even the same hard disk drive may also have the parameters slightly variable according to the respective heads and disks. Moreover, even the same disk may also have the parameters slightly variable according to an inner zone or outer zone. Therefore, it is necessary that a process for optimizing the read/write channel circuit 18 have the optimal parameters with respect to the respective zones and heads in the hard disk drive. Such a process is called the read channel optimization process.
Such an earlier read channel optimization process, as illustrated in FIG. 3, operates as follows. Referring to FIGS. 2 and 3, the microcontroller 24 reads from the memory 26 basic parameters that matches a currently selected zone and head, and supply the basic parameters to the read/write channel circuit 18 to set the respective circuit elements therein (step 100). The basic parameters are optimal parameters determined from a plurality of sample hard disk drives, prior to assembling the hard disk drive. The basic parameters are stored into the memory 26. Then, an off-track (i.e., a stress) is set to "0" (step 102), and a data read/write test is performed with respect to a given number of sectors for every track of the corresponding zone (step 104). Commonly, the data read/write test writes test data one time and reads the written test data several times. Then, a track having the minimum number of errors is selected for a track on which a channel optimization test is to be performed (step 106).
Thereafter, the microcontroller 24 performs the data read/write test while decreasing or increasing an off-track value beginning at an intermediate value between the maximum and minimum values (step 108). The microcontroller 24 determines an optimal off-track value having the maximum number of errors out of off-track values whose number of errors, i.e. the result of the data read/write test, falls within a predetermined reference value (step 110). The optimal off-track value becomes a test off-track value. Then, the microcontroller 24 performs the read/write test with respect to a predetermined number of sectors of the test track by predetermined parameter groups (step 112). The number of errors determined by the test result is then stored (step 114). The microcontroller 24 selects a level with the minimum number of errors for the optimal parameter (step 116) value with respect to the respective parameters.
The microcontroller 24 supplies the basic parameters to the read/write channel circuit 18 and performs the read/write test to determine the number of errors (step 118). Then, the microcontroller 24 supplies the selected optimal parameter value to the read/write channel circuit and perform the read/write test to determine the number of errors (step 120). Thereafter, the microcontroller 24 selects a better one of the test results for the optimal parameter value (step 122). Then, the optimal parameter value is stored in the memory 26 or written on a maintenance area of the disk 10 (step 122).
In case of a drive having a high error rate, the above mentioned process has a problem of taking a long time. Further, since the drives have different error rates, there will be a test time difference between a drive with a low error rate and a drive with a high error rate. In case an error is generated in a particular sector on the disk, the head commonly again reads data from the next sector. Thus, in order to read the data again from the next sector, the head must wait for one disk rotation time, i.e., a time for which the disk rotates in order for the next sector to return again to the head. Therefore, whenever the error is generated, the disk must make one rotation, resulting into an increase in the test time.
Further, as mentioned in the foregoing, in order to determine the optimal values of the respective parameters, the device must read the predetermined number of sectors, so that the drive with the high error rate may take a long time to test. Further, in case of the drive with the high error rate, the number of errors may exceed a reference value in spite of a low off-track value, so that it takes a long time to determine the test off-track value. Moreover, in order to set the test off-track value, the off-track value is tested beginning at the intermediate value between the maximum value and the minimum value. Thus, the test must be repeated until the off-track value reaches the minimum value. Accordingly, the drive with the high error rate will take a longer test time, compared with the drive with the low error rate. Further, the earlier device has a great test time difference according to the drives, so that it may not be easy to consider a proper countermeasure in a process for making the hard disk drive.